Squirrel-cage rotor

ABSTRACT

A squirrel-cage rotor has at least one laminated rotor core that has grooves and the squirrel-cage rotor has at least one rotor cage with electrically conductive rotor bars that are embedded in the grooves of the laminated rotor core in such a manner that the rotor bars have at their two end regions an overlap beyond the laminated rotor core, and the rotor cage has short-circuit rings that are attached at the end face to the laminated rotor core and have slots that are arranged in the region of their outer periphery and the end regions of the rotor bars protrude into said slots.

This application is a divisional of prior U.S. application Ser. No.14/828,694, filed Aug. 18, 2015, which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The invention relates to a squirrel-cage rotor for an asynchronousmachine, said squirrel-cage rotor having at least one laminated rotorcore that comprises a plurality of grooves and said squirrel-cage rotorhaving at least one rotor cage comprising electrically conductive rotorbars that are embedded in the grooves of the laminated rotor core insuch a manner that the rotor bars comprise at their two end regions anoverlap beyond the laminated rotor core, and said rotor cage comprisingshort-circuit rings that are attached at the end face to the laminatedrotor core and comprise a plurality of slots that are arranged in theregion of their outer periphery and the end regions of the rotor barsprotrude into said slots.

BACKGROUND OF THE INVENTION

The fundamental construction of squirrel-cage rotors for asynchronousmachines is generally known from the prior art. Various methods areknown for producing the rotor cage. In some cases, the entire rotor cageis cast in one piece. As a deviation from this, embodiments are knownwhere the rotor bars are produced from a semi-finished product and areembedded in the grooves of the laminated rotor core. The short-circuitrings are subsequently cast on. A further variant provides in contrastto this to produce the short-circuit rings from correspondingly formedmetal sheets. The metal sheets must have good electrically conductivecharacteristics and must be connected in a reliable manner to the rotorbars. This connection is formed in many cases by means of a solderingprocess, such as for example can be found in the document DE 34 21 537A1.

Furthermore, squirrel-cage rotors are known from DE 195 42 962 C1,wherein the short-circuit rings are constructed from copper metal sheetsand steel metal sheets that are positioned in an alternating manner withrespect to one another. As a consequence, the mechanical stability ofthe short-circuit rings is to be improved and the in-laid steel metalplates are to limit the extent to which the short-circuit ring canexpand even in the case of higher rotational speeds. The steel metalsheets are soldered to the copper metal sheets and the conductor bars.

It is proposed in the document DE 697 34 839 T2 to produce theshort-circuit rings of a cage rotor from a bimetal metal sheet, inparticular a steel-copper metal sheet. Bimetal short-circuit rings thatare produced in this manner are then positioned with their steel facetowards with the laminated rotor core, so that subsequently theshort-circuit ring can be welded to the laminated rotor core.

OBJECT OF THE INVENTION

The object of the invention is to provide an improved squirrel-cagerotor for an asynchronous machine. The improvement relates to theconstruction of the short-circuit rings and their connection to therotor bars.

The invention is characterized by the below discussed features,advantageous embodiments and further developments of the invention.

SUMMARY OF THE INVENTION

The invention includes a squirrel-cage rotor for an asynchronousmachine, said squirrel-cage rotor having at least one laminated rotorcore and having at least one rotor cage comprising electricallyconductive rotor bars and short-circuit rings. The laminated rotor corecomprises a plurality of grooves. The grooves can be embodied as groovesthat are open in the radial direction towards the exterior. The rotorbars are embedded in the grooves of the laminated rotor core in such amanner that they comprise at their two end regions an overlap beyond thelaminated rotor core. Short-circuit rings that comprise a plurality ofslots that are arranged in the region of their outer periphery areprovided on the end faces of the laminated rotor core and the endregions of the rotor bars protrude into said slots. The slots can beembodied as through-going openings that are open in the radial directiontowards the exterior or are closed. In accordance with the invention,the short-circuit rings comprise in each case at least two metalcomposite discs that for their part comprise at least one first metaldisc and a second metal disc that is connected in a planar manner tosaid first metal disc and is embodied from a different material thereto.Adjacent metal composite discs are arranged at least in part in such amanner that first metal discs of these metal composite discs are facingone another. The rotor rods are bonded, preferably welded, to the firstmetal discs in the region of the slots.

The invention is based on the consideration that the short-circuit ringsof the rotor cage comprise in each case a plurality of metal compositediscs. The metal composite discs comprise at least two metal discs thatare embodied from different materials and are connected one to the otherin a planar and electrically conductive manner. The materials of themetal discs differ from one another with respect to their density,electrically conductive characteristics, strength characteristics andtheir costs. Consequently the metal composite discs offer, in contrastto mono-metal discs, more freedom with regard to optimizing theshort-circuit rings with respect to the electrical conductance value,weight, strength and costs. The choice of the mutually combinedmaterials and the thickness ratio of the individual metal discs plays animportant role. The metal composite discs must be connected to the rotorbars at their end regions in an efficient electrically conductivemanner. The connection must be reliable and must not fail during theentire serviceable life of the machine even under the influence offorces such as during the operation of rapidly rotating components.Therefore, the connection between the rotor bars and the metal compositediscs is a bonded connection, by way of example by means of a solderingprocess or preferably by means of a welding process. Since it isdifficult to bond different metal materials to each other, the techniqueused to connect the rotor bars and short-circuit rings is selected suchthat essentially only the metal disc of a metal composite disc whosematerial can be best connected to the material of the rotor bars isconnected to the rotor bars. Within the scope of this invention, thismetal disc is described as the ‘first metal disc’ whereas a metal discthat is embodied from a different material thereto is described as the‘second metal disc’. The current is transferred from the rotor bars to ametal composite disc by way of the bonded connections initially to thefirst metal disc. The planar bond between the metal discs renders itpossible to transport the current within the metal composite disc with aminimum amount of electrical resistance. In accordance with theinvention, the metal composite discs of the short-circuit rings arearranged at least in part in such a manner that the first metal discs ofadjacent metal composite discs are facing one another. As a consequence,first metal discs, which are embodied from an identical material, ofadjacent metal composite discs are positioned directly next to oneanother. This is achieved in the case of metal composite discs thatcomprise two metal discs by virtue of the fact that adjacent metalcomposite discs are arranged in a mirror-inverted manner with respect toone another with regard to their disc arrangement. Alternatively,solutions using multi-layer metal composite discs are possible.

The particular advantage of this type of construction of short-circuitrings resides in the fact that two adjacent metal composite discs can beconnected to a rotor bar by means of a single connection process, by wayof example by means of a single welding procedure. Consequently, outlayand costs for connecting the short-circuit rings to the rotor bars canbe almost halved. Furthermore, it is possible to produce a reliableconnection between two adjacent metal composite discs without additionaloutlay. This improves the electrical conductivity of the short-circuitrings and increases the mechanical stability.

In a preferred embodiment of the invention, the rotor bars can beembodied at least in part from a material that can be easily welded tothe material of the first metal discs. It is possible to produceparticularly reliable connections by means of a welding process.Suitable connection methods are by way of example laser welding orelectron beam welding. The two materials that are welded one to theother preferably have melt temperatures or rather melt regions that areclose to one another and also similar thermally conductivecharacteristics. The difference in melt temperatures or rather weldregions is preferably a maximum 20 K.

In a particularly preferred embodiment of the invention, the rotor barscan be embodied at least in part from a material whose base material isidentical to the base material of the first metal discs. The twomaterials that are to be welded one to the other can therefore bedifferent alloys of the identical base material. The two alloys can inmany cases be easily welded as a result of the identical base material.In particular, the conductivity and the strength of a material can bepurposefully influenced by means of suitable alloying elements. It isthus possible by way of example to manufacture the rotor bars preferablyfrom an alloy that has a particularly high strength, whereas an alloythat has particularly good conductivity characteristics is used for thefirst metal discs of the short-circuit rings.

In an advantageous embodiment of the invention, the metal discs that areembodied from a different material and are part of the metal compositedisc are connected one to the other in a planar manner using a platingtechnique. The plating technique is a particularly suitable method ofconnecting different metal materials in a planar manner one to theother, said materials being available in a strip or sheet metal form. Aparticularly suitable method for this purpose is the laser roll platingtechnique. The plating method renders it possible to produce in afavorable manner semi-finished products that are embodied from metalcomposites, by way of example, bimetal strips. Semi-finished goods ofthis type can be metal composite discs that have been produced by meansof a suitable separating method, by way of example, stamping or lasercutting, and that are required in order to construct a short-circuitrotor in accordance with the invention.

In the case of an advantageous embodiment of the invention, the firstmetal discs can comprise at least one bevel on their outer periphery. Itis preferred that this bevel extends in the radial direction at least asfar as the slots. A bevel of this type provides the first metal discwith a geometry that is favorable for connecting to the conductor bars.The bevel produces a type of circumferential groove by means of which itis possible to access the connection site between the first metal discand the conductor bar. If a soldering process is used, the soldermaterial can be introduced into the groove and thus directed to theconnection site. If a welding process is used, energy can be introducedinto the weld site by means of the groove by way of example using aflame or a laser beam or electron beam.

In an advantageous embodiment of the invention, the first metal discs,in other words the metal discs that are bonded to the conductor bars,can be embodied from aluminum or an aluminum alloy. It is accordinglyadvantageous if the conductor bars are embodied at least in part fromaluminum or an aluminum alloy. As a result of their density and theirrelatively good electrically conductive characteristics, aluminum andaluminum alloys are preferred materials for conductor bars and shortcircuit rings of a cage rotor. In order in this advantageous embodimentto improve the electric conductance of the short-circuit rings, thesecond metal discs of the metal composite discs are preferably embodiedfrom copper or a copper alloy. As a consequence, a favorable compromisebetween electric conductance and weight is achieved. In a particularlyadvantageous embodiment of the invention, the thickness s₁ of the firstmetal discs is at least 60% of the thickness s of the metal compositediscs. The first metal discs are embodied from aluminum or an aluminumalloy. In comparison to other metal materials, aluminum is characterizedby virtue of a very low density and a favorable price in relation to itsvolume. If at least 60% of the metal composite discs are embodied fromaluminum or an aluminum alloy, then they are characterized by means of alow weight and low costs.

In the case of an alternative advantageous embodiment of the invention,the first metal discs, in other words the metal discs that are bonded tothe conductor bars, are embodied from copper or a copper alloy. It isaccordingly advantageous if the conductor bars are embodied at least inpart from copper or a copper alloy. As a result of their highelectrically conductive characteristics, copper and copper alloys arepreferred materials for conductor bars and short-circuit rings of asquirrel cage rotor. In order in the case of this advantageousembodiment of the invention to reduce the weight and the costs of theshort-circuit rings, the second metal discs of the metal composite discscan be embodied preferably in aluminum or an aluminum alloy. As aconsequence, a favorable compromise is achieved between electricalconductance, weight and cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further explained with reference to the followingexemplary embodiments and with reference to the schematic drawings, inwhich:

FIG. 1 illustrates a sectional view of a squirrel-cage rotor,

FIG. 2 illustrates an enlarged view of the view in FIG. 1 in the regionof the connection between the rotor bar and a short-circuit ring,

FIG. 3 illustrates an enlarged view of a further embodiment of asquirrel-cage rotor in accordance with the invention in the region ofthe connection between the rotor bar and a short-circuit ring.

Mutually corresponding parts are provided with the same referencenumeral in all figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a sectional view of a squirrel-cage rotor 1 inaccordance with the invention. The squirrel-cage rotor 1 has anessentially cylindrical shape with an axis A and a centrally arrangedbore hole 4 for receiving a shaft, not illustrated. Said squirrel-cagerotor comprises a laminated rotor core 11 that is constructed in amanner known per se from individual metal sheets. The laminated rotorcore 11 comprises a plurality of grooves 12, two of which are visible inthe sectional view. Furthermore, the squirrel-cage rotor 1 comprises aplurality of electrically conductive rotor bars 2, two of which arevisible in the sectional view, and also two short-circuit rings 3. Therotor bars 2 and the short-circuit rings 3 together essentially form thesquirrel cage. The rotor bars 2 are embedded in the grooves 12 of thelaminated rotor core 11 in such a manner that they comprise at their twoend regions 21 an overlap beyond the laminated rotor core 11. Generally,the rotor bars 2 are not arranged in parallel to the axis A of the cagerotor 1 but rather are arranged inclined by a defined angle of twistwith respect to the axis A. However, for reasons of clarity, thisfeature is not shown in the schematic illustrate in FIG. 1. The rotorbars 2 are embodied in the illustrated exemplary embodiment as solidmono-metal bars. However, it is also possible to use bi-metal barsand/or hollow bars. The short-circuit rings 3 are attached to the endfaces of the laminated rotor core 11. The short-circuit rings 3 comprisein the region of their outer periphery a plurality of slots 31. Thenumber and position of the slots 31 are to be selected such that saidslots can be brought into alignment with the grooves 12 of the laminatedrotor core 11. The end regions 21 of the rotor bars 2 protrude into theslots 31 of the short-circuit rings 3.

In accordance with the invention, the short-circuit rings 3 comprise ineach case four metal composite discs 32 that for their part comprise ineach case a first metal disc 33 and a second metal disc 34 that isconnected in a planar manner to said first metal disc and is embodiedfrom a different material thereto. In each case, two adjacent metalcomposite discs 32 are arranged in such a manner that the first metaldisc 33 or second metal disc 34 that are embodied from an identicalmaterial are facing one another. If you count for each of the twoshort-circuit rings 3 the metal composite discs 32 commencing at thefront face of the laminated rotor core, then in each case the second andthe fourth metal composite discs 32 are arranged in a mirror-invertedmanner with respect to the first and third metal composite disc 32. As aconsequence, in each case between the first and the second and alsobetween the third and the fourth metal composite disc 32, the firstmetal discs 33 that are embodied from an identical material are facingone another. Likewise, in each case between the second and the thirdmetal composite disc 32, the second metal discs 34 that are embodiedfrom an identical material are facing one another. In the schematicillustration of FIG. 1, adjacent metal composite discs 32 areillustrated for reasons of clarity in each case slightly spaced apartfrom one another. In reality, the metal composite discs 32 are generallypositioned without a spacing with respect to one another. Furthermore,it is possible that a spacing is provided between the laminated rotorcore 11 and the two metal composite discs 32 that are positioneddirectly adjacent to the laminated rotor core 11. The first metal discs33 comprise on their outer periphery a circumferential bevel 35 thatextends in the radial direction as far as the slots 31 of theshort-circuit rings 3.

By virtue of the identical hatchings of the elements that represent therotor bars 2 or rather the first metal discs 33 in FIGS. 1, 2 and 3, itis to be clarified that the rotor bars 2 and the first metal discs 33are preferably embodied from identical or similar materials. It isparticularly preferred that the rotor bars 2 and the first metal discs33 are embodied from aluminum or an aluminum alloy. As illustrated inFIG. 1, in this case the thickness s₁ of the first metal discs 33 is atleast 60% of the total thickness s of the metal composite disc 32. Inthe case of an alternative embodiment, the rotor bars 2 and the firstmetal discs 33 can be embodied from copper or a copper alloy.

The rotor bars 21 are bonded, preferably welded, to the first metaldiscs 33 in the region of the slots 31. This is further explained inconnection with FIG. 2.

FIG. 2 illustrates an enlarged section from FIG. 1 in the region of theconnection between a rotor bar 2 and the first metal discs 33 of ashort-circuit ring. A bonded connection 36 is produced in each case inthe region of the slots 31 between the first metal discs 33 and the endregion 21 of the rotor bar 2, illustrated in this case in a shortenedmanner. In the case of a solder connection, the connection 36 can be asolder material that fills a solder gap. In the case of a weldconnection, the connection 36 can be formed by means of a moltenmaterial of the mutually connected partners or by means of a weld fillermaterial. The two metal discs 34 and the rotor bar 2 are not bondedtogether, which is illustrated in FIG. 2 in each case by means of a gapbetween these components.

FIG. 3 illustrates an enlarged section of a further embodiment of asquirrel-cage rotor in accordance with the invention 1 in the region ofthe connection between a rotor bar 2 and a short-circuit ring 3. In thecase of this embodiment, the short-circuit ring 3 comprises two metalcomposite discs 32 that are arranged in a mirror-inverted manner withrespect to one another and comprise in each case a first metal disc 33and a second metal disc 34, and also metal composite discs 321 that arepositioned between said metal composite discs and comprise two firstmetal discs 33 and a second metal disc 34 that is arranged between twosaid first metal discs. In each case, a bonded connection 36 is providedin the region of the slots 31 between the first metal discs 33 of themetal composite discs 32 and 321 and the end region 21 of the rotor bar2, illustrated in this case in a shortened manner. Although the outlayfor producing metal composite discs 321 that comprise more than twometal discs 33, 34 is greater than when producing straightforwardbi-metal discs, the outlay involved in assembling the short-circuit ring3 is considerably reduced as a result of using this type of multi-layermetal composite discs 321. The embodiment in accordance with FIG. 3 canbe modified to the extent that more than one metal composite disc 321 isused, said one metal composite disc comprising two first metal discs 33and a second metal disc 34 that is arranged between the two first metaldiscs 33.

LIST OF REFERENCE NUMERALS

-   1 Squirrel-cage rotor-   11 Laminated rotor core-   12 Groove-   2 Rotor bar-   21 End region-   3 Short-circuit ring-   31 Slot-   32 Metal composite disc-   321 Metal composite disc-   33 First metal disc-   34 Second metal disc-   35 Bevel-   36 Connection-   4 Bore hole-   A Axis-   s Thickness of a metal composite disc-   s₁ Thickness of the first metal disc

What is claimed is:
 1. A method of manufacturing a squirrel-cage rotorfor an asynchronous machine, the squirrel-cage rotor having at least onelaminated rotor core that comprises a plurality of grooves, at least onerotor cage comprising electrically conductive rotor bars that areembedded in the grooves of the laminated rotor core in such a mannerthat the rotor bars comprise at their two end regions an overlap beyondthe laminated rotor core and short-circuit rings that comprise aplurality of slots that are arranged in the region of their outerperiphery, said method comprising the steps of: providing each of theshort-circuit rings with at least two metal composite discs thatcomprise at least a first metal disc and a second metal disc connectedto the first metal disc in a planar method through a plating process,the second metal discs being made of a different material from the firstmetal discs; arranging at least some of adjacent metal composite discsin such a manner that the first metal discs face one another; attachingthe short-circuit rings at the end face to the laminated rotor core, theend regions of the rotor bars protruding into said slots, and bondingthe rotor bars to the first metal disc in the region of the slots, twoadjacent metal composite discs be connected to a rotor bar through asingle connection process.
 2. The method according to claim 1,characterized in that the rotor bars are made at least in part from amaterial that can be easily welded to the material of the first metaldisc.
 3. The method according to claim 2, characterized in that therotor bars are made at least in part from a material whose base materialis identical to the base material of the first metal discs.
 4. Themethod according to claim 1, characterized in that the first metal discscomprise on their outer periphery at least one bevel.
 5. The methodaccording to claim 1, characterized in that the first metal discs aremade from aluminum or an aluminum alloy.
 6. The method according toclaim 5, characterized in that the thickness s₁ of the first metal discsis at least 60% of the thickness s of the metal composite discs.
 7. Themethod according to claim 1, characterized in that the first metal discsare made from copper or a copper alloy.